Epitaxial La0.7Sr0.3MnO3 thin films on silicon with excellent magnetic and electric properties by combining physical and chemical methods VILA-FUNGUEIRIñO J., GAZQUEZ J., MAGEN C., SAINT-GIRONS G., BACHELET R., CARRETERO-GENEVRIER A., Half-metallic ferromagnetic La0.7Sr0.3MnO3 (LSMO) represents an appealing candidate to be
integrated on silicon substrates for technological devices such as sensors, data storage media,
IR detectors, and so on. Here, we report high-quality epitaxial LSMO thin films obtained by an
original combination of chemical solution deposition (CSD) and molecular beam epitaxy
(MBE). A detailed study of the thermal, chemical, and physical compatibility between SrTiO3
(STO)/Si buffer layers and LSMO films, grown by MBE and CSD, respectively, enables a perfect
integration of both materials. Importantly, we show a precise control of the coercive field of
LSMO films by tuning the mosaicity of the STO/Si buffer layer. These results demonstrate the
enormous potential of combining physical and chemical processes for the development of
low-cost functional oxide-based devices compatible with the complementary metal oxide
semiconductor technology.×

Large anisotropy of ferroelectric and pyroelectric properties in heteroepitaxial oxide layers

Large anisotropy of ferroelectric and pyroelectric properties in heteroepitaxial oxide layers MOALLA R., CUEFF S., PENUELAS J., VILQUIN B., SAINT-GIRONS G., BABOUX N., BACHELET R., Epitaxial PbZr0.52Ti0.48O3 (PZT) layers were integrated on Si(001) with single PZT {001} orientation, mosaïcity below 1° and a majority of a-oriented ferroelectric domains (∼65%). Ferroelectric and pyroelectric properties are determined along both the out-of-plane and in-plane directions through parallel-plate capacitor and coplanar interdigital capacitor along the <100>PZT direction. A large anisotropy in these properties is observed. The in-plane remnant polarization (21.5 μC.cm−2) is almost twice larger than that measured along the out-of-plane direction (13.5 μC.cm−2), in agreement with the domain orientation. Oppositely, the in-plane pyroelectric coefficient (−285 μC.m−2.K−1) is much lower than that measured out-of-plane (−480 μC.m−2.K−1). The pyroelectric anisotropy is explicated in term of degree of structural freedom with temperature. In particular, the low in-plane pyroelectric coefficient is explained by a two-dimensional clamping of the layers on the substrate which induces tensile stress (from thermal expansion), competing with the decreasing tetragonality of a-domains (shortening of the polar c-axis lattice parameter). Temperature-dependent XRD measurements have revealed an increased fraction of a-domains with temperature, attesting the occurrence of a partial two-dimensional clamping. These observed properties are of critical importance for integrated pyroelectric devices. ×

Electric and mechanical switching of ferroelectric and resistive states in semiconducting BaTiO3-x films on silicon

Electric and mechanical switching of ferroelectric and resistive states in semiconducting BaTiO3-x films on silicon GOMES A., VILA-FUNGUEIRIñO J., MOALLA R., SAINT-GIRONS G., GAZQUEZ J., VARELA M., BACHELET R., GICH M., RIVADULLA F., CARRETERO-GENEVRIER A., Materials that can couple electrical and mechanical properties constitute a key element of smart actuators, energy harvesters, or many sensing devices. Within this class, functional oxides display specific mesoscale responses which often result in great sensitivity to small external stimuli. Here, a novel combination of molecular beam epitaxy and a water-based chemical-solution method is used for the design of mechanically controlled multilevel device integrated on silicon. In particular, the possibility of adding extra functionalities to a ferroelectric oxide heterostructure by n-doping and nanostructuring a BaTiO3 thin film on Si(001) is explored. It is found that the ferroelectric polarization can be reversed, and resistive switching can be measured, upon a mechanical load in epitaxial BaTiO3−δ/La0.7Sr0.3MnO3/SrTiO3/Si columnar nanostructures. A flexoelectric effect is found, stemming from substantial strain gradients that can be created with moderate loads. Simultaneously, mechanical effects on the local conductivity can be used to modulate a nonvolatile resistive state of the BaTiO3−δ heterostructure. As a result, three different configurations of the system become accessible on top of the usual voltage reversal of polarization and resistive states.×

Huge gain in pyroelectric energy conversion through epitaxy for integrated self-powered nanodevices MOALLA R., VILQUIN B., SAINT-GIRONS G., LE RHUN G., DEFAY E., SEBALD G., BABOUX N., BACHELET R., Polycrystalline (textured) and epitaxial 500 nm thick Pb(Zr0.52Ti0.48)O3 (PZT) layers have been monolithically integrated in metal-insulator-metal structure on silicon in order to compare their pyroelectric properties, both statically (under stabilized temperatures) and dynamically (when submitted to temperature transient as a pyroelectric device should work). The films have roughly the same out-of-plane orientation, and thus a similar out-of-plane remnant ferroelectric polarization around 12 μC/cm2. Whereas their static pyroelectric coefficients are similar (around −470 μC m−2 K−1), the dynamic pyroelectric coefficient of the epitaxial layer is about one order of magnitude larger than that of the polycrystalline layer (−230 vs −30 μC m−2 K−1). This causes an important difference on the densities of converted pyroelectric energy by almost two orders of magnitude (1 vs 1.5 10−2 mJ/cm3 per cycle for temperature variations of ∼6 K). This difference is explained here by the counterbalanced extrinsic pyroelectric contribution arising from the domain walls motion in the dynamical measurements. Extrinsic pyroelectric contribution appears almost twice larger on polycrystalline layer than on epitaxial layer (+430 vs +250 μC m−2 K−1). These results are crucial for further design of advanced integrated pyroelectric-based nanodevices.×

GaAs nanowires with oxidation-proof arsenic capping for the growth of an epitaxial shell

GaAs nanowires with oxidation-proof arsenic capping for the growth of an epitaxial shell GUAN X., BECDELIEVRE J., BENALI A., BOTELLA C., GRENET G., REGRENY P., CHAUVIN N., BLANCHARD N., JAURAND X., SAINT-GIRONS G., BACHELET R., GENDRY M., PENUELAS J., We propose an arsenic-capping/decapping method, allowing the growth of an epitaxial shell around the GaAs nanowire (NW) core which is exposed to an ambient atmosphere, and without the introduction of impurities. Self-catalyzed GaAs NW arrays were firstly grown on Si(111) substrates by solid-source molecular beam epitaxy. Aiming for protecting the active surface of the GaAs NW core, the arsenic-capping/decapping method has been applied. To validate the effect of this method, different core/shell NWs have been fabricated. Analyses highlight the benefit of the As capping-decapping method for further epitaxial shell growth: an epitaxial shell with a smooth surface is achieved in the case of As-capped–decapped GaAs NWs, comparable to the in situ grown GaAs/AlGaAs NWs. This As capping method opens a way for the epitaxial growth of heterogeneous material shells such as functional oxides using different reactors.×

Integration of functional complex oxide nanomaterials on silicon VILA-FUNGUEIRIñO J., BACHELET R., SAINT-GIRONS G., GENDRY M., GICH M., GAZQUEZ J., FERAIN E., RIVADULLA F., RODRIGUEZ-CARVAJAL J., MESTRES N., CARRETERO-GENEVRIER A., The combination of standard wafer-scale semiconductor processing with the properties of functional oxides opens up to innovative and more efficient devices with high value applications that can be produced at large scale. This review uncovers the main strategies that are successfully used to monolithically integrate functional complex oxide thin films and nanostructures on silicon: the chemical solution deposition approach (CSD) and the advanced physical vapor deposition techniques such as oxide molecular beam epitaxy (MBE). Special emphasis will be placed on complex oxide nanostructures epitaxially grown on silicon using the combination of CSD and MBE. Several examples will be exposed, with a particular stress on the control of interfaces and crystallization mechanisms on epitaxial perovskite oxide thin films, nanostructured quartz thin films, and octahedral molecular sieve nanowires. This review enlightens on the potential of complex oxide nanostructures and the combination of both chemical and physical elaboration techniques for novel oxide-based
integrated devices.×

Functional oxide pressure sensor LE BOURDAIS D., AGNUS G., MAROUTIAN T., PILLARD V., SAINT-GIRONS G., VILQUIN B., LEFEUVRE E., LECOEUR P., Manganites are well known in the oxide community, especially
La2/3Sr1/3MnO3 (LSMO) for its magnetic behavior above room temperature.
In these materials, electrical conduction is due to several phenomena such as
double exchange or polaronic conduction that give rise to a modulation of the
material’s resistivity with the temperature. Measuring the resistance of a device can thus be a way to measure its temperature and was notably used to design
bolometers working at room temperature, thanks to its high Temperature
Coefficient of Resistance (TCR) close to the ferromagnetic transition. For
suspended microdevices, dependence on the background gaz pressure is also
observed. This phenomenon relates to the Pirani effect where the surrounding
gas cools down the heated device because the local thermal conductivity
depends on ambient gas pressure. Close to the ferromagnetic transition, the
TCR of LSMO is almost a decade higher than Platinum making this material a
good candidate for sensor application at room temperature. Additionally, the
high chemical stability of manganites and their very low intrinsic electrical noise
level are other arguments to use them in this field. Micro-pirani sensors were
fabricated thanks to the integration of LSMO on Si with STO and YSZ buffer
following by MEMS technology processes. Such oxide-based sensors exhibit
sensitivity 10 times better and power consumption reduced by a factor of 100
with respect to a metallic sensor with the same geometry.×

Capping and decapping GaAs nanowires with As for preventing oxidation and for epitaxial shell growth

Capping and decapping GaAs nanowires with As for preventing oxidation and for epitaxial shell growth GUAN X., BECDELIEVRE J., BENALI A., BOTELLA C., GRENET G., REGRENY P., SAINT-GIRONS G., GENDRY M., PENUELAS J., Semiconductor nanowire-based materials are building blocks for future electronic and photonic devices. Due to their nanometric diameter and the efficient elastic relaxation at the lateral surface, nanowires (NWs) can accommodate more strain, and thus minimize lattice-matching constraints, inevitable in conventional thin film growth. In order to improve the physical properties of such nanowires and to develop electronic devices, core shell structure has been intentionally constructed. However preparing core/shell nanowires with good quality is quite challenging for the necessity of the perfect control of the core/shell interface. As known, oxidation is one of the most common processes which change the properties of the surface, in turn, affect the performance of materials. In consideration of the small dimension and the extreme large specific surface area, semiconductor NWs core materials have a higher tendency to be oxidized in the air, especially when an epitaxial shell made of heterogeneous materials is pursued which is obligated to be grown with a different reactor. However, the passivation preventing NWs from the oxidation is less studied.
In this work, self-catalyzed GaAs NWs were grown by molecular beam epitaxy (MBE) on silicon substrate. The morphology of NWs is uniform, about 50 nm in diameter and 1 μm in length, while the surface density is as high as 7 NW/μm2. To obtain a better understanding of the growth mechanism, the effect of different experimental parameters were investigated, including the effect of the substrate orientation (001), (111) and (110), the pre-deposition temperature of the catalyst, the gallium and arsenic flux and the temperature and time of the growth. Aiming to regrow an epitaxial shell around the as-prepared GaAs NWs in another reactor after an air exposure, chemical surface information on NWs was gathered by performing TEM and XPS measurements. A typical GaAs NW has quite smooth lateral facets with a thin amorphous layer outside which is composed of gallium and arsenic oxides, attributed to the oxidation in air. Such oxidation might affect the subsequent fabrication of the core-shell structure by introducing structural defects at the interface. Thus we propose a reversible arsenic-capping method without introducing any other impurities at the interface in order to exclude such difficulties. By using this method, the growth of shell materials is still under studied and will be reported later.×

Development of Epitaxial Oxide Ceramics Nanomaterials Based on Chemical Strategies on Semiconductor Platforms

Development of Epitaxial Oxide Ceramics Nanomaterials Based on Chemical Strategies on Semiconductor Platforms CARRETERO-GENEVRIER A., BACHELET R., SAINT-GIRONS G., MOALLA R., VILA-FUNGUEIRIñO J., RIVAS-MURIAS B., RIVADULLA F., RODRIGUEZ-CARVAJAL J., GOMES A., GAZQUEZ J., GICH M., MESTRES N., The technological impact of combining substrate technologies with the properties of functional advanced oxide ceramics is colossal given its relevant role in the development of novel and more efficient devices. However the precise control of interfaces and crystallization mechanisms of dissimilar materials at the nanoscale needs to be further developed. As an example, the integration of hybrid structures of high quality epitaxial oxide films and nanostructures on silicon as remains extremely challenging because these materials present major chemical, structural and thermal differences.
This book chapter describes the main promising strategies that are being used to accommodate advanced oxide nanostructured ceramics on different technological substrates via chemical solution deposition approaches. We will focus on novel examples separated in two main sections: (i) epitaxial ceramic nanomaterials entirely performed by soft chemistry, such as nanostructured piezoelectric quartz thin films on silicon or 1D complex oxide nanostructures epitaxially grown on silicon, and (ii) ceramic materials prepared by combining soft chemistry and physical techniques, such as epitaxial perovskite oxide thin films on silicon using the combination of soft chemistry and Molecular Beam Epitaxy (MBE).
Consequently, this chapter will cover cutting-edge strategies based on the potential of combining epitaxial growth and chemical solution deposition to develop oxide ceramics nanomaterials with novel structures and improved physical properties.×